Eggplant (Solanum melongena) is also know as Aubergine in British English. It is a member of the nightshade genus along with tomatoes. They come in a variety of colors and shapes and are quite versatile in the kitchen.
The original wild variety is small, with small berries looking like over-sized peas. These are intensely bitter, but are used in some areas (Thai green curry for example).
Wild Eggplant 
White Eggplant 
Purple Eggplant
Once domesticated, eggplants were bred for size and reduced bitterness. The name eggplant is derived from the appearance of cultivars that are white, slightly oval and about the size of an egg.
For more details, see: https://en.wikipedia.org/wiki/Eggplant